修改代码. 防止出错.

src/Editor/SelectControls.ts

@@ -161,6 +161,7 @@ export class SelectControls
             if (app.m_Viewer.m_GripScene.children.length > 0 && app.m_CursorViewer.m_LastSnapPoint)
             {
                 this.GridDrag();
+                return;
             }
 
             let pt = this.m_Editor.m_MouseCtrl.m_CurMousePointVCS;